This invention relates to a switching assembly for use with focussing, photosensitive elements which are used in a photographic camera, and more particularly, to such switching assembly for use with the camera of the type in which at least two interchangeable lenses having different brightness levels may be mounted and including at least two focussing, photosensitive elements associated with each of the interchangeable lenses.
A photographic camera of the TTL (through the lens) type is known (see Japanese Laid-Open Patent Application No. 143,404/1980) which permits a selective use of a first focussing, photosensitive element which permits the determination of an in-focus position in response to light from an object being photographed which is of a low brightness as transmitted through a taking lens of a relatively high brightness (for example, F2), and a second focussing, photosensitive element which permits such determination in response to light from an object being photographed which is transmitted through a taking lens of a relatively low brightness (for example, F4, such as telephoto lens). In such camera, each time a photographer mounts a different interchangeable lens on the camera, the type of the interchangeable lens is confirmed, and a corresponding focussing, photosensitive element is switched into a circuit. There are times when a photographer is so absorbed in the photographing operation that he will forget to constitute the switching operation even though another interchangeable lens has been mounted, thus leaving the photosensitive element associated with the old interchangeable lens in position into a circuit. This results in improper determination of an in-focus position.
A photographic camera of the TTL type is also known in which every interchangeable lens is provided with a signal pin for transmitting an electrical signal therethrough and which is arranged so that the pin may be utilized to effect an electrical switching between a plurality of focussing, photosensitive elements disposed within the camera (see Japanese Laid-Open Patent Application No. 144,211/1980). However, the switching arrangement in this pending application requires a complex construction and results in an expensive arrangement. In addition, the use of the usual interchangeable lenses having no signal pins is prevented, and thus the described switching arrangement is unavailable to the owner of such interchangeable lenses.